The present invention relates to an abrasive machine, more precisely relates to an abrasive machine having: a holding section for holding a wafer on a lower face; an abrasive plate having an abrasive face for abrading the wafer; and a driving mechanism for relatively moving the abrading plate with respect to the wafer.
These days, semiconductor devices are highly integrated, so flatness of silicon wafers, which will be substrates of semiconductor devices, must be highly improved. To precisely abrade layers and wires on a wafer, the surface of the wafer must be highly flat. Thus, machines for abrading wafers are required to highly precisely abrade surfaces of wafers and layers, etc. formed on the surfaces thereof. Besides wafers of semiconductor devices, high accuracy of abrading wafer-shaped work pieces is required in other fields.
Some conventional abrading machines have air bags, which are provided to the holding sections so as to uniformly press whole wafer faces onto the abrasive faces.
An example of the holding section 55 is shown in FIG. 4.
A head member 12 has a concave section 14 in a lower face thereof.
A holding plate 16 is provided in the concave section 14 of the head member 12, and a lower face is a holding face for holding a wafer 20.
A metallic bellows 56 is fixed between the holding plate 16 and the head member 12. The metallic bellows 56 allows the holding plate 16 to move close to and away from and incline with respect to the lower face of the head member 12. The metallic bellows 56 forms a pressure chamber 26.
In the holding section 55 having the above described members, the pressure chamber 26 is pressurized by supplying a pressurized fluid from pressurizing means (not shown) so as to press the wafer 20, with the holding plate 16, onto the abrasive face 50 of the abrasive plate 52.
The abrasive plate 52 is relatively moved with respect to the holding section 16 with the wafer 20 by a driving mechanism, so that the surface of the wafer 20 can be abraded by the abrasive face 50.
By employing the metallic bellows 56 in the holding section 55, the wafer 20 can be pressed onto the abrasive face 50 by pressing force, which is uniformly applied. And, the metallic bellows 56 can follow inclination and minute vertical movement of the abrasive face 50, therefore abrading accuracy of the abrasive machine can be improved. Further, the metallic bellows 56 can stand against external force, which is applied sideward, by its own rigidity.
However, the metallic bellows 56 is made by piling a plurality of donut-shaped plates and mutually welding their inner edges and outer edges. Therefore, it is difficult to uniformly welding their edges, so the wafer 20, which is held by the holding plate 16, cannot be uniformly pressed onto the abrasive face 52. And, the rigidity of the metallic bellows 56 is very high, so it cannot follow very minute change of pressure and motion. Further, the metallic bellows 56 causes liquation of metal ions, which must be avoided in the steps of manufacturing semiconductor devices.
To solve the above described disadvantages, as shown in FIG. 5, a holding section 60 includes an elastic member 62, which is, for example, a rubber plate, being fixed between the holding plate 16 and the head member 12 so as to form a pressure chamber 26, which allows the holding plate 16 to move close to and away from and incline with respect to a lower face of the head member 12.
The holding section 60 will be explained with reference to FIG. 5.
The abrasive plate 52 can be revolved on its own axis, and an abrasive cloth 51 is adhered on the abrasive plate 52 so as to form the abrasive face 50. The holding section 60, which is capable of revolving and vertically moving, is located above the abrasive face 50. The holding section 60 includes: a head member 12 having a concave section, which is opened in a lower face thereof; a holding plate 16 having a lower face capable of holding the wafer 20; the elastic member 62, whose outer circumferential part 62a is fixed to an inner bottom face of the head member 12 and whose inner circumferential part 62b is fixed to an upper face of the holding plate 16, suspending the holding plate 16 so as to allow very minute vertical and horizontal motion thereof; and the pressure chamber 26 being formed by dividing an inner space of the head member 12 with the holding plate 16 and the plate-shaped elastic member 62. A fluid supplying means (not shown) is communicated to the pressure chamber 26, so that pressurized fluid can be supplied into the pressure chamber 26. An O-ring 64 is made of, for example, rubber. The O-ring 64 is provided between the outer circumferential face of the holding plate 16 and the inner circumferential face of the concave section 14 of the head member 12, and it is capable of absorbing relative motion, e.g., rotation, swing motion, of the holding plate 16 with respect to the head member 12.
In the conventional abrasive machine, the elastic member 62, which is the rubber plate, makes the surface 20a of the wafer 20, which is adhered on the holding plate 16 by water, quickly follow minute inclination and minute vertical movement of the abrasive face 50 as the air bag. Even if the surface 20a follows the abrasive face 50, the whole surface 20a can be uniformly pressed onto the abrasive face 50. With this action, the whole surface 20a can be highly uniformly abraded like a mirror. Further, the disadvantage of the liquation of the metal ions can be solved.
Note that, in the holding section 60 shown in FIG. 6, the wafer 20 is adhered onto the holding plate 16 by water, so a backing sheet, whose surface has high adsorptivity, is adhered on the surface of the holding plate 16 so as to securely adhere the wafer 20 thereonto.
However, in the conventional abrasive machine, the holding plate 16 is suspended by one plate-shaped elastic member 62, so the whole surface of the holding plate cannot uniformly move, in the vertical direction, with enough stroke. Therefore, the holding plate 16 cannot fully follow the inclination and the vertical movement of the abrasive face 50, so that the whole surface 20a of the wafer cannot be uniformly pressed onto the abrasive face 50. Namely, the holding plate 16 does not have enough vertical stroke, so it can quickly follow the very minute movement of the abrasive face 50 but cannot follow when some conditions are changed. Especially, this disadvantage is serious in the case of precisely abrade large-sized wafers.
To solve this problem, using a rubber bellows instead of the elastic member 62 was proposed. But the elasticity of the rubber bellows is too high, so the rubber is irregularly deformed, and it is difficult to uniformly press the wafer 20 onto the abrasive face 50. Then, a rubber bellows reinforced by piano wires, etc. was used, but the rubber bellows cannot uniformly move because of the reinforcing member, so it is difficult to quickly and uniformly press the wafer 20 onto the abrasive face 50. It is also difficult to make the rubber bellows including the reinforcing members.
An object of the present invention is to provide an abrasive machine, which is capable of solving the liquation of metal ions, making a holding plate, which holds a wafer on a lower face, quickly follow very minute movement of an abrasive face of an abrasive plate, uniformly pressing the whole surface of the wafer onto the abrasive face, and improving abrading accuracy.
To achieve the object, the abrasive machine of the present invention comprises:
an abrasive plate having an upper face, which is an abrasive face capable of abrading a wafer;
a holding section including:
a head member being located above the abrasive face with a prescribed separation;
a holding plate being provided between the head member and the abrasive face, the holding plate having a lower face, which is a holding face capable of holding the wafer; and
a bellows being fixed between the holding plate and the head member, the bellows allowing the holding plate to move close to and away from and incline with respect to a lower face of the head member, the bellows forming a pressure chamber;
means for pressing the wafer onto the abrasive face, with the holding plate, by pressurizing the pressure chamber; and
a driving mechanism for relatively moving the abrasive plate with respect to the wafer held by the holding section so as to abrade the wafer by the abrasive face,
wherein the bellows is made by cutting a block of plastic without forming seams.
With this structure, no liquation of the metal ions is occurred; the holding plate, which holds the wafer on the lower face, can quickly follow the very minute movement of the abrasive face of the abrasive plate; the whole surface of the wafer can be uniformly pressed onto the abrasive face; and the abrading accuracy can be improved.
In the abrasive machine, the plastic may be ultra-high-molecular weight-polyethylene. With this structure, the bellows can have enough rigidity and can be easily made by cutting the plastic block
In the abrasive machine, the head member may have a concave section, which is opened in the lower face thereof, and the holding plate may be provided in the concave section of the head member, whereby an outer circumferential face of the holding plate contacts an inner circumferential face of the concave section so as to limit swing motion of the holding plate with respect to the head member. With this structure, the abrading accuracy can be improved.
In the abrasive machine, one of the outer circumferential face of the holding plate and the inner circumferential face of the concave section may be a convex face. With this structure, friction between the circumferential faces can be reduced, and the holding plate can be smoothly inclined or moved in the vertical direction.
The abrasive machine may further comprise:
means for reducing pressure in the pressure chamber;
a first tapered section being formed in the inner face of the concave section of the head member; and
a second tapered section being formed in the holding plate, the second tapered section being drawn and fitting with the first tapered section when the pressure in the pressure chamber is reduced,
wherein one of the first and second tapered sections are a male tapered section, and the other is a female tapered section. With this structure, the holding plate can be properly positioned, and the wafer can be precisely attached and detached.
In the abrasive machine, the holding face of the holding plate may be capable of sucking and holding the wafer by reducing pressure, or holding the wafer with water. With this structure too, the holding plate can be properly positioned, and the wafer can be precisely attached and detached.